Canada's biggest dairy producer said on Friday it is recalling Neilson Trutaste 2% Microfiltered Partly Skimmed Milk, sold in four liter bags, with a best-before date of February 12, 2012.

"Someone drank a bit of the milk and contacted us to let us know that she was suffering from a stomach ache," said Saputo spokeswoman Sandy Vassiadis.

Tests showed that the milk contained a cleaning product used to wash the tanks in the plant where the milk was processed. Vassiadis could not say what the cleaning product was.

"When mixed in with our milk in the concentration level that we were able to test, it could cause nausea, vomiting, a burning sensation, stomach aches," said Vassiadis.

The recall covers about 80,000 liters of milk, or one day's production, which was distributed in Ontario and Aylmer, Quebec. The Canadian Food Inspection Agency is monitoring the recall.

Vassiadis said the tank that handled the batch has been shut down while the company investigates what went wrong, although the rest of the facility is still in production.

Montreal-based Saputo produces and distributes milk, cheese and some baked goods. It operates nearly 50 plants in North America, South America and Europe.

Shares were down 0.65 percent at C$39.99 on Friday afternoon on the Toronto Stock Exchange.

(Reporting By Allison Martell; Editing by Peter Galloway and Janet Guttsman)

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